Component in Bitter Orange May Give Exercise a Fat-Burning Edge

Not getting the results you want from your workout? An alkaloid derived from bitter orange called p-synephrine, also found in Seville oranges, Nova tangerines, Marr's sweet oranges, and as an extract in dietary supplements, may help some people feel (and see!) the burn. A recent study, published in the British Journal of Clinical Pharmacology, found that p-synephrine may increase fat burn during low- to moderate-intensity exercise. For the double-blind study, researchers recruited 18 healthy, physically active participants, aged 18 to 33, to participate in two cycling trials with a three day rest period in between.

Both trials consisted of a ten minute warm-up, followed by a period of cycling in which participants sped up every three minutes until they voluntarily stopped from fatigue. An hour before one of the trials, participants took 3 mg of p-synephrine per kilogram of body mass; and an hour before the other trial, they took a placebo. Researchers measured the participants’ blood pressure, heart rate, oxygen uptake, and carbon dioxide production before the trials (while the participants were resting) and during the trials. They used the oxygen uptake and carbon dioxide production measurements to calculate each participants’ rate of calorie, fat, and carb burning, finding that:

During exercise, p-synephrine increased the rate at which fat burned by an average of 11% and reduced the rate at which carbs burned (compared with the placebo).

During exercise, p-synephrine didn’t affect blood pressure, heart rate, or the rate at which calories burned (compared with the placebo).

While the participants rested, p-synephrine didn’t affect the rate at which calories or fat burned (compared with the placebo).

These findings suggest that, if you’re healthy and active, p-synephrine may help you boost fat burn—without increasing your workout’s intensity; however, it's very important to note that this ingredient is a stimulant, and could therefore have potentially negative side effects. If you're interested in trying a supplement that contains p-synephrine, be sure to consult with your healthcare practitioner first to find out if it’s right for you.